Battery packs including a plurality of batteries accommodated in a case, and capable of outputting predetermined voltage and current are widely used as power sources of various devices, vehicles, etc. Specifically, a technique in which general-purpose batteries (for example, cylindrical secondary batteries used in notebook computers) are connected together in parallel and/or in series to obtain modules of battery assemblies for outputting predetermined voltage and current, and these battery modules are combined together to be applicable to various applications, is beginning to be used. This modular technique can reduce the size and weight of the battery modules themselves by increasing the performance of the batteries accommodated in the battery modules. Thus, this modular technique has various advantages, such as an increase in workability in assembling a battery pack, and improvement in flexibility in mounting the battery module in areas of limited space, such as a vehicle.
Here, if a battery included in the battery module becomes unable to serve as a battery due to overcharge or overdischarge, or due to an internal short-circuit or external short-circuit, the abnormal battery may function as a resistor, and the performance of the battery module as a whole may be reduced significantly.
In view of this problem, Patent Document 1 discloses a battery assembly in which a plurality of series cell units, each including a plurality of cells connected in series, are connected in parallel. In this battery assembly, a resistor is provided between the cells adjacent to each other in the parallel direction. In this structure, in the event that an abnormal condition, such as an internal short-circuit, occurs in a cell, the resistor can reduce a current which flows into the abnormal cell.
However, since the abnormal cell cannot be disconnected from the battery assembly in this structure, it is not possible to sufficiently prevent a reduction in performance of the battery assembly as a whole.
In view of this, Patent Document 2 discloses a battery assembly in which a plurality of series battery groups, each including a plurality of batteries connected in series, are connected in parallel. In this battery assembly, a current bypass circuit is connected in parallel to each of the series battery groups, and a fuse is connected in series to each of the series battery groups and the current bypass circuit. In this structure, in the event that an abnormal condition occurs in a cell, the abnormal condition is detected and a high current is supplied to the current bypass circuit battery to melt the fuse, thereby making it possible to disconnect the series battery group including the abnormal battery from the battery assembly.
However, in this structure, the number of components may be increased because the current bypass circuit which operates when an abnormal battery is detected needs to be provided for each of the series battery groups. Further, since the batteries adjacent to each other in the parallel direction are not connected to each other in parallel, battery charge condition in charging the battery assembly may vary according to the series battery groups, which may lead to a reduction in performance of the battery assembly as a whole.
In view of this problem, Patent Document 3 discloses an assembled battery in which a plurality of batteries are connected together in parallel via connecting members. In this assembled battery, the positive electrode and the negative electrode of each of the batteries are connected to the connecting member by a fusible link. In this structure, in the event that an abnormal condition occurs in a battery, the fuse connected to the abnormal battery is melted due to overcurrent. Thus, the abnormal battery can be electrically disconnected from the other batteries.